Pilot bit for earth augers



INVENTOR. Gem/a 4 fieze/se/z Filled Nov. 1, 1949 G A PETERSEN PILO'I BIT FOR EARTH AUGERS May 19, '1 953 Patented May 19, 1953 UNITED STAT ES PAT OFF-ICE" PILOT'BIT FOR EARTH AUGERSL GeraldA. Petersen, San Francisco; Cam: ApplicatiomNovember 1, 1949, Serial No. 124 8818 3 v 1 Claim. (Cl. 255-f-61) In power boring of earth holes particularly in ground that is irregular-in make up andin characteristics, it .is necessary to have-a pilot bit for the earth auger which excavates cleanly, which clears itself of the materials being excavated, which wears extremely well, since it is normally the first to encounter abrasive material, and especially one which is capable of digging or excavating at least as fast as the remainder of the auger can excavate once the initial path has been broken.

It is an objectof my invention to provide an improved pilot bit for earth augers which'will have the various attributes mentioned above.

Another object of my invention is to provides. pilot bit for earth augers effective over along period of time, with little deteriorationdue' to abrasion and wear andefiective to operate with moderate power at relatively great speed.

Another object of my invention is to provide a pilot bit for an earth auger eifectively usable with earth augers already available.

Another object of my invention is to provide a pilot bit effective to operate in various different soils normally encountered.

A still further object of my invention is to provide a pilot bit readily handled by workmen under the usual conditions and readily fabricated for economical production.

Other objects, together with the foregoing are attained by the embodiment of the invention described in the accompanying description and illustrated in the accompanying drawings in which:

Figure 1 is a side elevation of my pilot bit as it is provided for attachment to an earth auger.

Figure 2 is a top plan view of the pilot bit as shown in Figure 1.

Figure 3 is a bottom plan view of the pilot bit as shown in Figure 1.

While it is susceptible to use in many different environments and can be readily varied within the scope of the claims to meet different circumstances in use, my pilot bit is especially useful in conjunction with an earth auger of the type shown in my co-pending application entitled Earth Auger, filed August 5, 1946, Serial No.

688,436, new Patent;2,578,014,. issued'December 11, 1951. Thatearth auger includes a-rotary member having a central tubewith a non-circular cross section designedto be driven by a squared shaft from a suitable power source and at the bottom includes anattachmentmeans for a pilot bit, the pilotbit being approximateiya quarter thediameter-of themain auger.

In the I present, instance. the earth. auger is represented in broken linesas having acentral sleeve 6 pierced by, asquare or rectangular central passageway l. and. designed to, rotate. about a longitudinal axis 8. Designed to. fit inthe sleeve 6 is my pilot bit. This bitincludes a. shank portion alargely circular in its outline although having. a. pair of flatsidesll and.v Theshank includes a cross key: l3 designedxtointerfit ina suitable transverse slot in the bottom of the drive ing sleeve 6 andincludesfurthermore-a central tongue l4 extendin upwardly. into. the. bore. of the sleeve 6,. Thepilot .bit is "fastened inplaee byathrough pin, [6 engaging the sleeve and also passing through an aperture ll. piercing. the tongue. This attachment/is readily, made when the pilotbit is first.assembledwiththe. earth augerso thatthepilot bit-is held in-placeand iscaused to rotate with theearthaugerebout .the axis 8., When .itis-tobe removed-,thepilot bit is readily detached after withdrawal of the pin l6.

Preferably formed integrally with the shank 9 and in most instances cast in one piece therewith are blade members 2! and 22, respectively. In the present instance, two blade members are disclosed as representative of any chosen number and since each of the blade members is identical with the others the description of one applies equally to the others. The blade member 22, for example, depends from the shank 9 in a generally downward direction, as seen in Figure 1, and as it descends or depends, it advances in the direction of rotation of the bit as a whole, as represented by the arrow 23. The path of the surface or contour of the blade member 22 is approximately helical although it deviates from a true mathematical helix in that its cross-section in any plane normal to the rotational axis is a right line in advance of a line through the axis 8 in that plane.

The blade 22 terminates on its leading, cutting edge 24 in a plane, represented by the line 26 in Figure 1, that is normal or perpendicular to the axis 8. The leading edge 24 is a straight or right line in the plane 26 and is spaced or displaced from a line 21 (Figure 3) passing through the axis 8 by a predetermined amount 28, the direction of displacement being in the direction of advance as indicated by the arrow 23. The leading edge 24 does not extend as far as the axis 8 itself but, being displaced from such axis, is in fact tangent to an imaginary circle 29 having the axis 8 as a center and disposed in the plane 26.

The shape of the blade member 22 is such that the blade is relatively thick throughout most of its length but adjacent its leading edge 24 rapidly thins so that the line trace results. Furthermore the leading edge 24 does not extend for a full diameter 3| of the hole 32 bored by the bit. Rather, the leading edge 24 extends inwardly to a point 33 approximately on the tangent circle 29 at which point the envelope curve of the blade member extends inwardly and upwardly along an approximately helical line 34, as seen in Figure 1, to provide a central V-shaped, relieved recess symmetrical about the axis 8 of the bit. The outer margin 36 of the blade member 22 may either lie on the periphery of the hole 32, or may recede from the leading edge 24 toward the center in a spiral plan, as shown in Figure 3.

In operation when the pilot bit is on an earth auger and is rotated in the direction of the arrow 23, the leading edges 24 of the blades 21 and 22 advance into and cut the earth not with a straight ahead motion but rather with a component which is transverse or lateral so that a shearing action takes place and an annular path is cut. The central portion of the pilot bit near the v-shaped central notch defined by the edges 34 does not cut but rather breaks the earth away as the bit advances. It has been found that this is a superior means for removing the central part of the bore. The material which has been removed by the combination advancing and shearing or sliding cutting action rides upwardly over approximately helical surfaces of the blade members 2| and 22 and travels upwardly into the earth auger from which it is discharged.

A pilot bit constructed as indicated is cheap to manufacture since it is cast in a single piece, is readily mounted an demounted by workmen at the site with the customarily available tools, by virtue of its shearing action wears a long time '4 relatively under all sorts of digging conditions, and because it is relieved at its center advances rapidly into the earth without being held back by a central block and provides a generally improved operation for devices of this sort.

I claim:

A pilot bit for earth augers comprising a shank adapted to rotate in a predetermined direction about an axis to bore a hole of predetermined circumference, a pair of identical blade members depending from said shank, each of said blade members having a helical leading surface generated throughout its length by a right line moving in a downward direction in a substantially helical curve, said line being tangent to a small circle concentric with said axis and located between the perimeter of said bore and said axis, said leading surface terminating in a leading edge disposed in a plane perpendicular to said axis on a right line tangent to said small circle, said leading edge extending from said small circle to a point on said circumference of said hole, the outer margins of said blade members receding from said points on said circumference to a lesser diameter in a spiral plan as said margin ascends from said leading edge.

GERALD A. PETERSEN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 504,018 Caldwell Au 29, 1893 1,373,996 Clore Apr. 5, 1921 1,791,186 Black Feb. 3, 1931 1,882,268 Appleman Oct. 11, 1932 1,897,733 Ormsby et al. Feb. 14, 1933 1,945,159 Pearce Jan. 30, 1934 2,025,354 Maschek Dec. 24, 1935 2,372,612 Stogsdill Mar. 27, 1945 FOREIGN PATENTS Number Country Date 373,642 Germany Apr. 14, 1923 600,676 Germany July 28, 1934 394,890 Great Britain July 6, 1933 500,147 Great Britain Feb. 3, 1939 

